you dont have to run 64-bit os on a 64-bit machine, indeed i would think most people are still running 32-bit for better compatiblity (or not knowing any better!). 64-bit [windows] does mean you can throw a boot load of ram at the machine (abnd it can actually use it ;-)) whereas 32bit is limited to just over 3gb...

you dont have to run 64-bit os on a 64-bit machine, indeed i would think most people are still running 32-bit for better compatiblity (or not knowing any better!). 64-bit [windows] does mean you can throw a boot load of ram at the machine (abnd it can actually use it ;-)) whereas 32bit is limited to just over 3gb...

It's not just compatibility that makes 32bit better than 64bit. 32bit tends to perform faster (tighter exe's being the main reason) and 32bit has a much lower memory overhead than 64bit - so much so, in fact, that apps running in either native or emulated 64bit on a 64bit OS tend to consume around 20-25% more memory than the 32bit equivelents on a 32bit OS. Mathematically, this means that the amount of data that a 32bit OS and a 64bit OS both with 4GB of RAM installed can access is slightly greater on a 32bit OS. Under the 32bit OS, you lose around 768MB virtual address space and other memory, whereas under 64bit OS, while all the memory in the system can be accessed, it's in such an inefficient manner that you're effectively losing ~900MB to memory overheads. So unless you're using apps that need more than 3GB of memory to function properly, there's very little point using a 64bit OS.

Me, by the way, I use Vista Ultimate 64 on my main desktop system (6GB), and Server 2008 32 on my livingroom system (2GB). All is good.